Twisted strands and non-woven filtering media made of such strands



NOV. 7, 1967 c BUTLER ET AL 3,351,205

TWISTED STRANDS AND NON'WOVEN FILTERING MEDIA MADE OF SUCH STRANDS FiledMay 18, 1962 4 Sheets-Sheet 1 Fi i INVENTORS i I3 CLRREm: R. Bu'rLEmm jlj Dominic R. LRZZHRO A" V A /ans, fig? files 1Q [4 HT OKNEYS Nov. 7,1967 c. A. BUTLER ET AL 3,351,205 TWISTED STRANDS AND NON-WOVENFILTERING MEDIA MADE OF SUCH STRANDS Filed May 18, 1962 INVENTORS 4Sheets-Sheet 2 CLRRENCE B ,ku-ruzn. rmo

Dominic R Lnzzmzo @5028, i HT ORNEY5 Nov. 7, 1967 c. A. BUTLER ET AL'3,351,205 TWISTED STRA AND NONWOVEN FILTERING MEDIA E OF SUCH STRANDSFiled May 18, 1962 4 Sheets-Sheet 3 /7 mm/ m Fj 14 l5 fj lli $5 1 7 2e30 32' 6 Q as 30 I 15 F i? EEG "Fail E1 E3 7 T f4 FE .55

INVENTORS K 5 CLHRENCE R. BUTLER, Dommic R. LRZZFIRO Nov. 7, 1967 QBUTLER ET AL 3,351,205 TWISTED STRANDS AND NON-WOVEN FILTERING MEDIAMADE OF SUCH STRANDS Filed May 18, 1962 4 Sheets-Sheet 4 INVENTORSCumuce Rjuuap Dominic R. Lnzznao NEYS United States Patent Ofifice3,351,205 Patented Nov. 7, 1967 3,351,205 TWlSTEl) STRANDS AND NON-WOVENFILTER- llNG MEDIA MADE OF SUCH STRANDS Ciarence A. Butler and DominicRichard Lazzaro, Cleveland, Ohio, assignors to The Lindsay Wire WeavingCompany, Cleveland, Ohio, a corporation of Ohio Filed May 18, 1962, Ser.No. 197,168 The portion of the term of the patent subsequent to Dec. 1,1981, has been disciairned Claims. (Cl. 219-490) This invention relatesto non-woven filtering media comprised of twisted strands, and themethod of making such media. The invention is adapted for use as afilter either for general use or for making belts and the like for usewith paper-making machines.

Heretofore, it has been experienced that the wire mesh conventionallyused in making Fourdrinier belts for use in paper-making machines musthave certain hydraulic characteristics of porosity, as well assufi'icient wear resistance, corrosion resistance, and durability inorder to provide the optimum desired operational conditions for makingpaper. In the past, the utilization of a coarse wire mesh resulted in aquick tie-watering of the thin fiber mat formed on the belt causing thefine material to flow out as white water before formation of the mat onthe belt. Under these conditions, the paper sheet was found to be moredense over the wires than in the area between the wires, resulting in awire mark in the sheet itself, which could not be brushed or pressed outof the sheet. Thus, it was considered that the ideal sheet formingconditions for uniform structure are to have the thin fiber mat formedrapidly on a belt to prevent the loss of fine material and to keep thestock on the belt fluid for a sufiicient time. In the case of woven wirebelts, eiforts to meet these requirements resulted in using finer meshwires and by attempting to drive more shute wires into the screen todecrease the open area between wires. However, such efforts to make asuperior sheet by putting more metal into the belt or making it finerhave been unsatisfactory due to the increased expense of finer wire, andrelatively shorter life of such wire. More importantly, fabrics, Whethermade of natural fibers, synthetic fibers, or metallic wire, when woven,depend on the openings in the weave for porosity, since the fibers orwires generally extend in a direction of One of the planes of the fabricor the belt. Even when the fabric is woven of a twisted yarn, theindividual fibers or wires, themselves being non-porous or of lowporosity, produce no passageways substantially perpendicular to theplane of the fabric resulting in extremely poor and uncontrolledhydraulic characteristics essential to the production of a superiorpaper sheet.

Therefore, an object of the present invention is to provide twistedstrands for use in making non-woven filtering media having improvedcharacteristics of porosity, wear resistance, corrosion resistance, anddurability.

Another object of the present invention is to provide twisted strandscomprised primarily from thermoplastic material suitable for use inmaking non-woven fabric, belts, and the like suitable for use with papermaking machines having improved characteristics of porosity, wearresistance, corrosion resistance, and durability.

'A further object of the present invention is to provide a non-wovenfiltering media comprised of twisted strands and the method of makingsuch media having improved characteristics of porosity, wear resistance,corrosion resistance, and durability.

A still further object of the present invention is to provide anon-woven filtering media comprised primarily of twisted thermoplasticstrands, and the method of making such media for use in paper-makingmachines having improved characteristics of porosity, wear resistance,corrosion resistance, and durability.

Another object of the present invention is to provide a non-woven beltof twisted strands suitable for use with paper-making machines havingimproved characteristics of porosity, wear resistance, corrosionresistance and durability.

A still further object of the present invention is to provide anon-woven belt made primarily from thermoplastic twisted strandssuitable for use with paper-making machines having improvedcharacteristics of porosity, wear resistance, corrosion resistance anddurability.

An additional object of the present invention is to provide a moreeconomical, light weight, non-woven fabricor belt, comprised primarilyof thermoplastic twisted strands suitable for use with paper-makingmachines having improved characteristics of porosity, wear resistance,corrosion resistance and durability.

Other and further objects of the present invention will be apparent fromthe following description and claims illustrated in the accompanyingdrawings, which, by way of illustration, show a preferred embodiment ofthe present invention and the principles thereof and what is nowconsidered to be the best mode in which to apply these principles. Otherembodiments of the invention embodying the same or equivalent principlesmay be applied by those skilled in the art in structural changes may bemade as desired without departing from the scope of the presentinvention, in the drawings:

FIG. 1 is an enlarged fragmentary plan view showing a non-wovenfiltering media comprised of the twisted strands embodying the presentinvention;

FIG. 2 is a cross sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary plan view showing a modification ofthe non-woven filtering media comprised of twisted strands embodying thepresent invention;

FIG. 4 is a cross sectional view taken along lines 4 4 of FIG. 3;

FIG. 5 is an enlarged fragmentary plan view showing another modificationof the non-woven filtering media comprised of a twisted strand embodyingthe present invention;

FIG. 6 is a cross sectional view taken along lines 6-6 of FIG. 5;

FIG. 7 is an enlarged fragmentary plan view showing another modificationof the non-woven filtering media comprised of the twisted strandsembodying the present invention;

FIG. 8 is a cross sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is an enlarged fragmentary plan view showing a non-wovenfiltering media comprised of a plurality of layers of twisted strandsembodying the present invention;

FIG. 10 is an enlarged fragmentary plan view showing a modification of anon-woven filtering media comprised of a plurality of layers of twistedstrands embodying the present invention;

FIG. 11 is an enlarged fragmentary plan View showing a non-wovenfiltering media comprised of twisted strands in conjunction withsupporting strands embodying the present invention;

FIG. 12 is a sectional view showing a twisted strand having areinforcing element extending therein;

FIG. 13 is a sectional view showing a modification of the twisted strandhaving a filler material formed therein as a reinforcing means;

FIGS. 14 through 34 inclusive are vertical cross sectional views showingmodified shapes of the twisted strands embodying the present invention;

FIG. 35 is a perspective view of a non-Woven endless belt made inaccordance with the principles of the present invention;

FIG. 36 is a diagrammatic illustration showing the filtering mediaembodying the present invention passing between spaced pairs of rollsfor expanding the media longitudinally in accordance with the principlesof the present invention;

FIG. 37 is a diagrammatic illustration showing the filtering mediaembodying the present invention, in another form, mounted intermediateclamping members for expanding the media in transverse and longitudinaldirections in accordance with the principles of the present invention;

FIG. 38 is a diagrammatic illustration showing an endless belt made fromthe filtering media embodying the present invention mounted on stretcherrolls for expanding the belt longitudinally in accordance with theprinciples of the present invention.

Generally, we have found that a filtering media having improvedcharacteristics of porosity, wear-resistance and corrosion-resistancemay be obtained by forming such media of a plurality of twistedthermoplastic strands. By varying the cross sectional configuration,amount and direction of twist of such strands in accordance with theprinciples of the present invention, we provide a filtering media havinga predetermined specific surface area and an improved porosity which issubstantially perpendicular to the plane of the media. Accordingly, byforming a filtering media of twisted strands, there is achieved acontrolled porosity through the media which is not dependent on theporosity of the strands themselves nor upon intricate weavingtechniques, as in the case of conventional fabric constructions.Moreover, in addition to providing a filtering media for general use, wemay provide such a media for making endless belts or the like which aresuitable for use with paper-making machines. For example, by twistingthe thermoplastic strands and maintaining a predetermined ratio ofspecific surface area to drainage area, there is obtained an endlessbelt which provides a more efficient utilization of paper stock whileincorporating optimum drainage characteristics for producing a superiorpaper product.

In addition, it has been found that materials, such as thermoplastics,when expanded under controlled temperature condit-ions provide strengthand durability highly suitable for making endless belts or the like forpaper-making machines. Moreover, expanding of various thermoplastics,such as polycarbonate and nylon, in accord with the principles of thepresent invention, results in a preferred orientation of the molecularchains comprising the plastic and in the direction of expansion. Suchorientation of the plastic not only provides a substantial increase instrength and durability but upon such orientation, the plastic willretain its final dimension, as expanded. Accordingly, we have found thatby forming a filtering media of a plurality of such thermoplastictwisted strands and by subsequently expanding the media under controlledtemperature conditions, there is achieved a controlled variation in theopen area between adjacent twisted strands such as to provide afiltering media having optimum hydraulic characteristics suitable foruse, for example, as belts or the like for paper-making machines.

Briefly, to accomplish the objects of providing a filtering media havingimproved characteristics of porosity, wear resistance, corrosionresistance and durability, there may be provided a non-wovenconstruction made of a plurality of twisted strands having predeterminedcross sectional configurations. The twisted strands may be joinedtogether into one or more layers and in a manner to provide apredetermined specific surface area and a porosity through the layer orlayers that may be substantially perpendicular to the plane of themedia.

To further increase the strength of the media and to maintain a constantporosity through the openings formed between adjacent twisted strands,the filtering media may then be subjected to an expanding operation toorient the strands a predetermined amount in the direction of expansion.In some cases, additional layers of strands of the same and/0r largercross-sectional dimensions may be utilized in conjunction with thefiltering media to provide a more durable construction when utilized,for example, in the environment of paper-making machines.

Referring now more particularly to the drawings, FIGS. 1 to 4 illustrateone form of the invention, wherein fiat strands 1-2-1, respectively, maybe formed into a single layer by fusion, solvent cementing or by meansof adhesives, such as shown generally at 8 of FIG. 2. In this form, theindividual strands, before being bonded together, may be twisted andheat set in a manner and in an amount suflicient to provide the desiredspecific surface and porosity without overstressing the individualstrands. As shown, the alternative strands 1 may be twisted aboutonehalf or about with about five turns per inch of length in acounterclockwise direction, while the intermediate strands 2 may betwisted the same amount in the opposite or clockwise direction, wherebythe openings 9 formed between adjacent strands are aligned in rowsextending substantially transversely across the plane of the filteringmedia. FIGS. 3 and 4 show another form of the invention, wherein thestrands 3-4-3, respectively, may be of a generally cross-shape incross-section, whereby the openings 10 between adjacent strands areconsiderably more numerous but are of a relatively smaller dimension. InFIGS. 6 and 5, the strands 5-6-5, respectively, may be semicircular inform having a channel portion in vertical crosssection, whereby theopenings 11 between adjacent strands may be alternatively spaced orstaggered transversely across the width of the filtering media.

In another form, FIGS. 7 and 8 illustrate a construction wherein theL'shaped strands 7-7-7, respectively,

may be twisted with about five turns per inch of length in the samedirection either clockwise or counterclockwise. In this forrn, thealternate strands of the layers may also be shifted longitudinally withrespect to the intermediate layers by an amount sutficient to producethe openings 12 to obtain a desired porosity. It is to be understood,however, that in some cases, it maybe desirable to, twist the adjacentalternative strands in a manner to vary the relative pitch of the strandrather than by shifting the strands in order to obtain the desiredporosity between adjacent strands, as aforementioned. Asshown at FIGS. 9and 10, the non-woven filtering media may be formed having more than onelayer of twisted strands. In such case, the media may include an upperlayer of strands 3-4-3, which may extend at an angle with respect to thestrands 3 -4 -3 of the lower layer in order to effect the desired degreeof porosity through the openings in the layers. In this form, thetwisted strands 3-4-3, of the upper layer may extend longitudinally andat right angles. or perpendicularly with respect to the twisted strands3 -4 -3 of the lower layer, to provide the desired degree of porosityand a predetermined amount of specific surface area, as shown a at FIG.10.

FIGS. 11 to 13 illustrate another form of the invention, wherein strands13 may be utilized as supporting or carrying elements for the filteringstrands 7 under conditions where the strands of the filtering media donot have sufficient strength to perform the necessary mechanicalfunctions for sufiicient life and durability. Such a condition, forexample, may exist where a coarser mesh filtering media is required. Asshown, the carrying strands 13 may extend transversely relative to thefabric or media and may be provided, with a reinforcing means, suchasmetallic wires, glass strands or the like, shown generally at 15 ofFIG. 11. In another form, shown at FIG. 13, the carrying strands 13 maybe impregnated with between about 20 to 40 percent, by weight, of afiller material 14, such as glass flakes comprised of borosilicate orthe like,.to impart the desired reinforcing strength to the filteringmedia. In this regard, it is to be understood that the carrying membersmay extend longitudinally rather than transversely with respect to thefiltering media in order to provide the necessary durability for suchmedia. In cases where it is desirable to utilize a supporting layer inconjunction with the filtering media, the strands 13 may be of a greatercross-sectional dimension relative to the strands of the filtering mediato thereby impart a greater durability to the media or fabric.

To further control the specific area and porosity through the openingsformed between adjacent twisted strands, the filtering media may beprovided with additional strands having various cross-sectionalconfigurations, best shown at 19 of FIGS. 1 and 2. As shown, the strands19 may extend longitudinally between the alternate strands 1 and theintermediate strands 2 in a manner to overlie the openings 9 formedbetween the adjacent strands. In this manner, in addition to controllingthe porosity between openings by a predetermined twisting of theindividual strands comprising the media, such porosity may also becontrolled by decreasing the area of the openings by the attachment ofsuch additional strands to the media. Moreover, the additional strands19 are preferably of a finer cross-sectional dimension and may or maynot be twisted, as desired, to achieve a predetermined porosity throughthe filtering media.

The strands comprising the filtering media, fabric, belt or the like,may be formed in any predetermined shape which is suitable forincreasing the specific surface area of the belt and which will providethe necessary porosity between adjacent strands of the media. Typicalshapes which are useful for such strands are indicated generally atFIGS. 14 through 34, inclusive. FIG. 14 illustrates a quadrilateralconfiguration in vertical cross-section in the form of a fiat ribbonhaving side portions 16 and 17. FIG. 15 shows a similar configurationhaving rounded ended portions 18. FIG. 16 shows the strands as beinggenerally parabolic, or in the form of a double concave in verticalcross-section, having oppositely disposed concave side portions 20. FIG.17 shows the strands as comprising two generally circular portions 22and 24 bonded together to define a generally figure-eight configurationin vertical cross-section. FIG. 18 shows the strands to be of agenerally cross-shaped configuration in vertical crosssection havingfour oppositely disposed arm portions 26. FIG. 19 shows a similarconfiguration wherein the arms 26 are generally rounded 28 at their freeends. FIG. 20 shows the strand as being generally star-shaped invertical cross-section having oppositely disposed points 30. FIG. 21shows a similar configuration wherein the points 30 may be rounded 32 attheir free ends. FIG. 22 shows a modification of the cross-shapedconfiguration wherein four individual strands 34 may be bonded togetherto form the desired configuration. Similarly FIG. 23 shows amodification of the star-shaped configuration wherein four individualstrands 36 may be equally spaced and bonded together, as illustrated.FIG. 24 shows the strands to be of a generally L-shaped configuration invertical cross-section having two leg portions 38 extending atsubstantially right angles to one another, whereas, in FIG. 25 the freeends of the leg portions may be generally rounded, as at 40. FIG. 26shows a triangular configuration, in vertical cross-section, having twoside portions 42 which may be closed across their free ends by agenerally surpentine portion 46. FIG. 27 shows a right triangularconfiguration in vertical cross section having side portions 48 and 5!}extending at right angles from one another enclosed across their ends bythe side portion 52 in the form of a hypotenuse. FIG. 28 shows amodification of the triangular configuration as being generallytruncated in vertical cross section having a base portion 54, angularlyinwardly extending side portions 56 and a generally fiat or rounded topportion 58. FIG. 29 shows the strand as being generally semi-circular 60in vertical cross-section, whereas FIG. 30 illustrates the semi-circularconfiguration as being provided with a generally rounded, longitudinallyextending channel portion 62. FIG. 31 shows the strand as beinggenerally U-shaped in vertical cross section, having a base portion 64and two generally vertical upstanding flange portions 66. FIG. 32 showsthe strand as being of a generally star-shaped 68 configuration inradial cross section having six oppositely disposed lobes 70. FIG. 33shows a similar starshaped configuration 72 having three evenly spacedlobes 74 whose center lines lie at an obtuse angle with respect to oneanother. FIG. 34 shows the strand to be of a dumbbell configuration 76having a reduced portion 78 located intermediate two enlarged endportions 80.

In a like manner, where carrying strands are to be used in conjunctionor in combination with the filtering media to impart greater durabilityto the strands, the aforementioned or similarly shaped strands may beutilized as carrying members to obtain the desired specific surface andthe required porosity between strands. In this regard, and for purposesof definition, the generally noncircular cross-sectional configurationapproximating the circular form may be referred to in terms of a closedplane curve, such as, for example, the elliptical and parabolicconfigurations. Other regular and/or irregular configurations may bereferred to in terms of a closed plane having at least one includedangle, such as, for example, the triangular, quadrilateral and polygonalconfigurations. As applied to the making of non-woven endless belts forpaper making machines, the various crosssectional shapes of the twistedstrands shown in the drawings are preferably of a size which may becircumscribed by a circle having a diameter of between about 0.010 inchand 0.130 inch. The degree of twist whether in the clockwise orcounterclockwise direction may vary with the extent of specific surfacearea and porosity required in the desired filtering media. For example,a twist embodying five turns per inch of length would be suitable forobtaining a satisfactory ratio of specific surface area to porosity fora filter which would be included within the scope of this invention.

The method of making such filtering media, fabric, belts and the like byattachment of one strand to another may be accomplished by one orseveral methods. For example, the attachment may be achieved by use ofsolvent cementing, therrnofusion techniques, or by the use of suitableadhesives, such as those known in the art.

toreover, the thermofusion techniques may be accomplished by directapplication of heat through heated platens, rollers, or by generatingthe heat within the strands themselves, by high frequency dielectricheating, or ultrasonics, or by the use of heated air or liquids. Ifdesired, pressure may be utilized in conjunction with the aforementionedthermoheating techniques, or with solvent cementing. In this connection,it is to be noted that another important advantage may be obtained byfabrication of non-woven media, fabrics, and belts from twisted strands,such as shown at 9% of FIG. 35. For example, the production of anendless belt is facilitated because the ends of the carrying strands, orthe filtering strands, as the case may he, need not be joined at thesame transverse location, hence, there is no need for a straight linejoint or seam extending directly across the transverse portion of thebelt. By attaching the ends of the strands together, at staggered pointstransversely of the belt, such as shown at 72 of FIG. 1, the inherentdisadvantages of a single joint, or seam, are eliminated, therebyallowing the production of a fabric or a belt having improved durabilityand dependability in operation.

In accord with the principles of the present invention, any material,whether made of natural fibers, synthetic fibers, or metallic wireshaving the desired characteristics of wear resistance, corrosionresistance, and durability, which may be formed and twisted into thedesired strand configuration may be suitable for making such non-wovenfiltering media. We have found, however, that some thermoplasticmaterials are particularly suitable for making such non-woven filteringmedia, particularly when utilized in making endless belts for papermaking machines. Such thermoplastic materials may include cellulosenitrate, cellulose acetate, cellulose acetate-butyrate, polystyrene,polyethylene, polycarbonate, polypropylene, linear polyethylene,polyvinyl chlorine, vinyl esters, vinylidene chloride, styreneacrylonitrile, styrene butadiene, polytetrafiuorethylene,polychlorotrifluoroethylene, acrylonitrile resin rubber, nylon, methylmethacrylate, ethyl cellulose and the like.

Preferred among the above mentioned thtrmoplastic materials arepolycarbonate and nylon which have the property that when expanded underthe proper temperature conditions, the molecular chain, of which theplastic is comprised, becomes oriented in the direction of expanding,thus greatly increasing the strength of the material. In order that thedesired result be obtained, the molecular chains must have sufiicientmobility so that they are free for movement and become aligned withneighboring molecular chains of the composition. In cases where heat maybe applied to the material to promote such mobility, the preferredtemperature is commonly referred to as the glass transition temperature.Conversely, when the glass transition temperature is exceeded for asubstantial length of time, such as in the normal use of an endlessbelt, in paper making operations, the orientation and beneficial effectsof such orientation become reduced or are lost.

Moreover, when a material, such as polycarbonate, is expanded to produceorientation at temperatures for that material within the glasstransition temperature of be tween 250 F. to 310 F. and is subsequentlyused at temperatures substantially below the lower operating limit of250 F. for that material, the strength of material is not onlyincreased, but the preferred orientation of the material is retained andthe material does not return to its original shape prior to suchexpansion. Accordingly, to obtain the desired molecular orientation ofthe material, it is preferable that the glass transition temperature ofthe material be kept substantially above the maximum temperature atwhich the material may be subjected in actual use. In this regard, andfor purposes of definition, when reference is made to the glasstransition temperature, we refer to the temperature demarcation betweenthe lower temperature wherein individual molecules of the plasticmaterial remain relatively fixed and the higher temperature wherein theindividual molecules are free for movement relative to one another.

Expanding of the twisted strands to provide the desired molecularorientation of the thermoplastic material may be accomplished in one ofseveral modified forms. As shown at FIG. 36, the individual twistedstrands may be attached together to form the desired filtering media,shown diagrammatically at 81. In this form, the media may be stretchedlongitudinally between a first pair of oppositely disposed rollers 82and a second pair of similar rollers 83 which may be actuated forrotation in the same direction, but which are coordinated to rotate athigher predetermined speeds relative to the first pair of rollers. Suchrelative rotational speeds between the respective pairs of rollersallows the thermoplastic filtering media passing between the rollers tobe expanded and oriented to any predetermined amount, as desired.

In another form, as shown at FIG. 37, the filtering media 81 may bestretched by gripping the edge portions of the media between pairs ofoppositely disposed clamping members 84 and 86, which may be secured tothe media by suitable fastening means 85. To stretch the media, theclamping members may be actuated by suitable mechanical or motor powermeans (not shown) to cause the members to move away from one another, asshown by the arrows, whereby the media may be expanded in a transverseand/ or longitudinal direction, as desired.

Moreover, in another form, the filtering and/ or carrying strands may beattached together by means of the aforementioned thermofusion or solventcementing techniques to form an endless belt, shown generally at of FIG.38. In this form, the belt 90 may be mounted as a unit on oppositelydisposed stretcher rolls 92, which are adapted for longitudinal movementtoward and away from one another, as shown by the arrows, to impart thedesired amount of expansion to the individual thermoplastic strandscomprising the belt.

In this regard, though we have illustrated several modilied forms bywhich the fabric or belt may be expanded, it is to be understood that insome cases it may be desirable to expand the individual strands prior toattaching them together as a unitary filtering media or belt. Forexample, when the strands are twisted cold or under controlledtemperature conditions there results, to some extent, a molecularorientation of the thermoplastic material. We have found it preferable,however, to expand the twisted strands under controlled temperatureconditions when attached together either as a fabric, or in the form ofan endless belt, whereby we are able to obtain a greater uniformity inorientation of the thermoplastic material. The amount of expanding ofthe thermoplastic may vary in each case depending upon the desiredmolecular orientation of the material, and upon the spacing between thetwisted strands required to produce hydraulic characteristics suitablefor a given paper making operation. We have found, for example, that byattaching a thermoplastic material, such as a polycarbonate, to betweenabout 80 to of its initial length and at a temperature within the glasstransition temperature of between 250 to 310 F. for that material, thereis obtained desired orientation and drainage characteristics suitablefor making Fourdrinier belts.

It can be seen from the foregoing description that the filtering mediacomprised of non-woven twisted strands, results in many importantadvantages. Such a filtering media has the important advantage of beingconstructed to provide the necessary physical strength to insureprolonged life and durability in conjunction with a specific surface,which may be made as fine as desired, depending upon the particular useto which the media may be applied. In such case, by twisting the strandsand/ or by arranging the stranded layers into predetermined non-woven.

patterns, there is achieved an increased specific surface area and animproved porosity through the passageways formed by the strands which issubstantially perpendicular to the plane of the media.

Accordingly, by twisting strands having cross-sectional configurationsother than round, there is achieved a controlled porosity through theopenings formed between adjacent strands which is not dependent upon thespacing of the strands themselves but which may be predetermined by thedegree of twist given to the individual strands.

In the case of the utilization of such media in the making of endlessbelts for paper making machines, there results a controlled filtrationof the paper stock formed on the belt, while at the same time reducingthe loss offine materials through the belt. It can be seen, therefore,that by maintaining a predetermined ratio between specific surface areaand drainage area, there is obtained an endless belt which provides amore efficient utilization of paper stock while incorporating optimumdrainage characteristics for producing a superior paper product.

Though we have selected to illustrate the principles embodying thepresent invention with reference to the fabrication of Fourdrinierbelts, it is to be understood that the construction may also be appliedto other similar applications. The application of such constructions mayvary in use from a filter or separator for liquids and solids, to

a construction which may be substantially impervious to moisture butwhich will allow the easy passage of air or gas.

Thus, while we have illustrated herein a preferred embodiment of ourinvention, it is to be understood that changes and variations may bemade by those skilled in the art without departing from the spirit andscope of the appended claims.

We claim:

1. An endless, non-Woven fabric belt for use with Fourdrinier type ofpaper making machines adapted for draining fluent material, such aspaper stock, formed thereon, said fabric belt comprising a firstsubstantially co-planar layer of polymeric mono-filament strandsextending generally parallel to one another and longitudinally of thebelt, a second substantially co-planar layer of polymeric mono-filamentstrands extending generally parallel to one another and transversely atan angle relative to said first layer, said first and second layers ofstrands being disposed in superimposed relationship and bonded togetherat their areas of contact between the respective strands in each of saidlayers, the strands in each of said layers having a non-circulartransverse cross-section and being independently twisted a predeterminednumber of turns in a generally circular direction along their axes, andthe strands in each of said layers being disposed in continuousside-by-side relationship and bonded to each other throughout theirlength at their areas of contact to form longitudinally extending rowsof spaced openings between adjacent strands in each of the respectivelayers.

2. A fabric belt in accordance with claim 1, wherein alternate strandsin each of said layers are twisted a predetermined number of turns inone circular direction along their axes, and the intermediate strandsare twisted a predetermined number of turns in the opposite circulardirection along their axes.

3. A fabric belt in accordance with claim 1, wherein the strands in eachof said layers are twisted a predetermined number of turns in the samecircular direction along their axes.

4. A fabric belt in accordance with claim 1, including a solid polymericmono-filament strand disposed between and extending generally parallelbetween adjacent twisted strands in one of said layers, said solidstrands having a substantially reduced transverse cross-sectionaldimension as compared to the greatest cross-sectional dimension of saidtwisted strands in said layer so as to only partially overlie the rowsof longitudinally extending openings formed between adjacent of saidstrands in said layer.

5. A fabric belt in accordance with claim 1, wherein the strands in eachof said layers have been twisted approximately five turns per inch in acircular direction along their axes.

References Cited UNITED STATES PATENTS 2,919,217 12/1959 Bobkowicz16l143 X 3,063,094 11/1962 Warthen 161177 X 3,095,283 6/ 1963 Wheeler29-191.6 3,158,984 12/1964 Butler 1-61177 X FOREIGN PATENTS 5,762 1897Great Britain.

MORRIS SUSSMAN, Primary Examiner.

EARL M. BERGERT, ALEXANDER WYMAN,

Examiners.

L. T. PIRKEY, G. D. MORRIS, Assistant Examiners.

1. AN ENDLESS, NON-WOVEN FABRIC BELT FOR USE WITH FOURDRINIER TYPE OFPAPER MAKING MACHINES ADAPTED FOR DRINING FLUENT MATERIAL, SUCH AS PAPERSTOCK, FORMED THEREON, SAID FABRIC BELT COMPRISING A FIRST SUBSTANTIALLYCO-PLANAR LAYER OF POLYMERIC MONO-FILAMENT STRANDS EXTENDING GENERALLYPARALLEL TO ONE ANOTHER AND LONGITUDINALLY OF THE BELT, A SECONDSUBSTANTIALLY CO-PLANAR LAYER OF POLYMERIC MONO-FILAMENT STRANDSEXTENDING GENERALLY PARALLEL TO ONE ANOTHER AND TRANSVERSELY AT AN ANGLERELATIVE TO SAID FIRST LAYER, SAID FIRST AND SECOND LAYERS OF STRANDSBEING DISPOSED IN SUPERIMPOSED RELATIONSHIP AND BONDED TOGETHER AT THEIRAREAS OF CONTACT BETWEEN THE RESPECTIVE STRANDS IN EACH OF SAID LAYERS,THE STRANDS IN EACH OF SAID LAYERS HAVING A NON-CIRCULAR TRANSVERSECROSS-SECTION AND BEING INDEPENDENTLY TWISTED A PREDETERMINED NUMBER OFTURNS IN A GENERALLY CIRCULAR DIRECTION ALONG THEIR AXES, AND THESTRANDS IN EACH OF SAID LAYERS BEING DISPOSED IN CONTINUOUS SIDE-BY-SIDERELATIONSHIP AND BONDED TO EACH OTHER THROUGHOUT THEIR LENGTH AT THEIRAREAS OF CONTACT TO FORM LONGITUDINALLY EXTENDING ROWS OF SPACEDOPENINGS BETWEEN ADJACENT STRANDS IN EACH OF THE RESPECTIVE LAYERS.